The above-referenced patent application and prior U.S. Pat. No. 4,004,299 both disclose cardiac pumping devices in which the rotation of a spiral driver produces linear movement of a follower assembly which, during movement in one direction, compresses two blood compatible sacs which simulate the left ventricle and right ventricle of the heart by pumping blood through the aorta and pulmonary artery, respectively. In the prior art devices, return movement of the follower assembly in terms of rate is a function of right atrial and left atrial pressure and volume. Stroke volume of each simulated ventricle is independent of the other as in the natural heart. In the device of the pending application above-referenced, the mechanism automatically adjusts its rate of pumping in accordance with both preload (filling pressure) and afterload (pulmonic and systemic pressure), and in addition modifies its stroke volume in a downward direction when confronted with high afterload. This automatic adjustment of the device during operation depends on several variables and is accomplished without electronic control or monitoring.
The present invention, while possessing all of the attributes of the above two prior art devices, is a special adaptation thereof to provide a left atrial to descending thoracic aorta left ventricle assist device. In achieving this objective, the basic drive means of the prior patent and pending application are utilized in conjunction with a thin walled rectangular cross-section compression chamber for a Dacron pouch which extends through the chamber and is equipped beyond the ends of the chamber with a pair of porcine valves and conduit extensions which are connected to the left atrium and the descending thoracic aorta, respectively.
Within the compression chamber is a flat rectangular ejection plate having a pivot lug near the lower or aortic end thereof for pivotal connection with one drive leg of a follower ring housing which surrounds the spiral drive shaft or element. Near its upper or left atrial end, the ejection plate carries a laterally projecting pivoted extension pin equipped at its free end with a spring. The extension pin and spring are received in a tubular leg of the follower ring housing and the spring can bottom in this leg. In response to linear displacement of the ring follower housing, the end of the ejection plate proximal to the left atrium is first forced into compressive engagement with the Dacron pouch by the action of the extension pin-spring connection with said tubular leg. Subsequently, during further movement of the ring follower housing, both ends of the ejection plate are equally and fully moved into compressive engagement with the Dacron pouch to force a predetermined volume of blood from the left atrium to the pouch and into the descending thoracic aorta.
Other features and advantages of the invention will become apparent during the course of the following description.